1. Field of the Invention
The present invention relates to disk drive performance features and more particularly to a disk drive having a cache control system for improving the disk drive's response to host commands.
2. Description of the Prior Art
A host computer stores and accesses data on a disk drive by issuing commands to the disk drive over a standardized interface. The smallest indivisible data unit addressable on a disk is a logical block or disk sector, typically of 512 bytes, and each such disk sector is assigned a logical block address (LBA). When the host computer sends a command to the disk drive, the nature of the command is specified, e.g., read or write, along with a start LBA and a count specifying the number of contiguous sectors to be transferred.
Existing disk drives typically have a semiconductor cache memory for temporarily storing disk data that is likely to be requested by a host computer. The response time latency for storing and accessing data in a semiconductor memory is much smaller than the response time latency for mechanically storing and accessing data stored on a rotating disk. In existing disk drives, if an entire LBA range of a host command is not found, or if the first LBA of the host command is not buried within a segment or range of LBA's stored in the cache memory, then a new cache segment is configured for responding to the host command. Accordingly, although the LBA range of the host command may overlap with the LBA range of a segment of the cache memory, that segment is essentially useless in responding to the host command.
Accordingly, there exists a need for a disk drive having a cache memory that may be configured to advantageously use existing cached data to respond to a host command. The present invention satisfies these needs.